BIODEGRADATION OF PARAQUAT BY BACTERIA-IMMOBILIZED BIOCHAR IN AQUEOUS SOLUTION

Abstract

The work studied the isotherm, kinetic and mechanism of Paraquat adsorption in aqueous solution by using corncob biochar produced from different pyrolysis temperatures and times. The kinetic and isotherm data was fitted by the Pseudo-second-order and Langmuir models. These results showed that the adsorption capacity decreased with increasing pyrolysis temperatures during 6 hours in the order 200, 300, 400, 500, 600oC and decreasing pyrolysis time in the order 2, 3, 4, 5, 6 hours, respectively at 200oC. The mechanisms possibly contributed to hydrogen bonding and pore filling while π-π interaction was minor contributor in the adsorption process. Therefore, the corn cob biochar can become an alternative and promising adsorbent for Paraquat removal from an aqueous solution.

Furthermore, the study explored the isotherm, kinetic and mechanism of paraquat adsorption in aqueous solution by coconut fiber (CFB), corn cob (CCB), bagasse (BGB) and rice husk (RHB) biochars.The biochar characteristics were identified using SEM, BET, and FTIR. Kinetic and isotherm data were followed the Pseudo-second-order and Langmuir models. The biochars were arranged according to their capacity: CFB (12, 72 mg/g), CCB (10.27 mg/g), RHB (9.72 mg/g), BGB (7.79 mg/g) where specific surface area and pore volume determined the adsorption capacity. The intraparticle diffusion model was used to assess the kinetic rate of the adsorption process, which indicates the rate constant of the external diffusion phase where Kip1 was higher than the Kip2 and Kip3 phases. Film diffusion played a major role in the adsorption process. Pore filling, diffusion, hydrogen bonding, π-π and electrostatic interactions contributed to the mechanism of adsorption. CFB has the highest adsorption capacity (12.72 mg/g), and can be an alternative adsorbent.

From this work, the study aims to explore the isotherm, kinetic and mechanism of paraquat adsorption in aqueous solution by free and immobilized cells of Pseudomonas putida on corn cob biochar using three methods: the adsorption method, the covalent bonding method and the entrapment method. The characteristics of bacteria and biochar were studied using SEM, BET. The results shown that kinetic and isotherm data were followed the Pseudo-second-order and Langmuir models. The covalent bonding method was the best immobilization cell method with PQ removal at 4.21 mg/g. Moreover, the PQ adsorption capacity of living cells (3.15 mg/g) is higher than the PQ adsorption capacity of dying cells (2.41 mg/g). The intermediate products such as 4,4-bipyridyl (m/z 155) and malic acid (m/z 133) are detected in the effluent of samples (free cells, fixed cells on CCB, CFB, BGB, RHB using entrapment, covalent binding and adsorption methods) was collected at 35 h experimental period for analysis Paraquat products by GC/MS. The experiment was set up at the optimal operational concentration of Paraquat being 25.73 mg/L. The study encircles biodegradation of paraquat by bacteria immobilized biochar in aqueous solution. The discovery of these intermediate products sheds light on the specific degradation pathways of paraquat and may provide valuable information for developing effective strategies for the remediation of paraquat contaminated environments.

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